[Mono WASM + AOT] `Environment.Exit` does not work together with exception handling

[SingleAccretion]

Reproduction:

dotnet new wasmconsole

Program.cs:

Console.WriteLine("Running...");
try
{
    Environment.Exit(100);
}
finally
{
    Console.WriteLine("Oops");
}

Expected (module the missing JS symbols file):

dotnet run ; Will run under interpreter

MONO_WASM: Error loading symbol file dotnet.native.js.symbols: {}
Running...

Actual:

dotnet publish /p:RunAOTCompilation=true -c Release /p:WasmNativeStrip=false

node main.mjs

Running...
Error: [MONO] * Assertion at /__w/1/s/src/mono/mono/mini/interp/interp.c:2756, condition `<disabled>' not met

    at ht (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12516)
    at bt (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12770)
    at wasm_trace_logger (wasm://wasm/04dd8aba:wasm-function[33399]:0x5ac684)
    at eglib_log_adapter (wasm://wasm/04dd8aba:wasm-function[22319]:0x3d7c26)
    at monoeg_g_logv_nofree (wasm://wasm/04dd8aba:wasm-function[22213]:0x3d3fcc)
    at monoeg_assertion_message (wasm://wasm/04dd8aba:wasm-function[22217]:0x3d40ff)
    at mono_assertion_message (wasm://wasm/04dd8aba:wasm-function[22219]:0x3d4146)
    at mono_assertion_message_disabled (wasm://wasm/04dd8aba:wasm-function[22218]:0x3d4117)
    at do_jit_call (wasm://wasm/04dd8aba:wasm-function[21558]:0x3b10f4)
    at mono_interp_exec_method (wasm://wasm/04dd8aba:wasm-function[21548]:0x3a4de7)
Error: [MONO] * Assertion at /__w/1/s/src/mono/mono/mini/interp/interp.c:2756, condition `<disabled>' not met

    at ht (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12516)
    at bt (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12770)
    at wasm_trace_logger (wasm://wasm/04dd8aba:wasm-function[33399]:0x5ac684)
    at eglib_log_adapter (wasm://wasm/04dd8aba:wasm-function[22319]:0x3d7c26)
    at monoeg_g_logv_nofree (wasm://wasm/04dd8aba:wasm-function[22213]:0x3d3fcc)
    at monoeg_assertion_message (wasm://wasm/04dd8aba:wasm-function[22217]:0x3d40ff)
    at mono_assertion_message (wasm://wasm/04dd8aba:wasm-function[22219]:0x3d4146)
    at mono_assertion_message_disabled (wasm://wasm/04dd8aba:wasm-function[22218]:0x3d4117)
    at do_jit_call (wasm://wasm/04dd8aba:wasm-function[21558]:0x3b10f4)
    at mono_interp_exec_method (wasm://wasm/04dd8aba:wasm-function[21548]:0x3a4de7)

Cause: I did not confirm this 100%, but highly suspect the cause to be the fact that EH as emitted by the AOT compiler is translated into WASM's catch_all. catch_all catches all exceptions, even JS ones thrown by Emscripten's exit.

Although, curiously enough, a -c Debug publish, seemingly not using WASM EH, also crashes.

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Reproduction:

dotnet new wasmconsole

Program.cs:

Console.WriteLine("Running...");
try
{
    Environment.Exit(100);
}
finally
{
    Console.WriteLine("Oops");
}

Expected (module the missing JS symbols file):

dotnet run ; Will run under interpreter

MONO_WASM: Error loading symbol file dotnet.native.js.symbols: {}
Running...

Actual:

dotnet publish /p:RunAOTCompilation=true -c Release /p:WasmNativeStrip=false

node main.mjs

Running...
Error: [MONO] * Assertion at /__w/1/s/src/mono/mono/mini/interp/interp.c:2756, condition `<disabled>' not met

    at ht (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12516)
    at bt (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12770)
    at wasm_trace_logger (wasm://wasm/04dd8aba:wasm-function[33399]:0x5ac684)
    at eglib_log_adapter (wasm://wasm/04dd8aba:wasm-function[22319]:0x3d7c26)
    at monoeg_g_logv_nofree (wasm://wasm/04dd8aba:wasm-function[22213]:0x3d3fcc)
    at monoeg_assertion_message (wasm://wasm/04dd8aba:wasm-function[22217]:0x3d40ff)
    at mono_assertion_message (wasm://wasm/04dd8aba:wasm-function[22219]:0x3d4146)
    at mono_assertion_message_disabled (wasm://wasm/04dd8aba:wasm-function[22218]:0x3d4117)
    at do_jit_call (wasm://wasm/04dd8aba:wasm-function[21558]:0x3b10f4)
    at mono_interp_exec_method (wasm://wasm/04dd8aba:wasm-function[21548]:0x3a4de7)
Error: [MONO] * Assertion at /__w/1/s/src/mono/mono/mini/interp/interp.c:2756, condition `<disabled>' not met

    at ht (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12516)
    at bt (file:///C:/Users/Accretion/source/investigation/BrowserConsole/bin/Release/net8.0/browser-wasm/AppBundle/_framework/dotnet.runtime.js:3:12770)
    at wasm_trace_logger (wasm://wasm/04dd8aba:wasm-function[33399]:0x5ac684)
    at eglib_log_adapter (wasm://wasm/04dd8aba:wasm-function[22319]:0x3d7c26)
    at monoeg_g_logv_nofree (wasm://wasm/04dd8aba:wasm-function[22213]:0x3d3fcc)
    at monoeg_assertion_message (wasm://wasm/04dd8aba:wasm-function[22217]:0x3d40ff)
    at mono_assertion_message (wasm://wasm/04dd8aba:wasm-function[22219]:0x3d4146)
    at mono_assertion_message_disabled (wasm://wasm/04dd8aba:wasm-function[22218]:0x3d4117)
    at do_jit_call (wasm://wasm/04dd8aba:wasm-function[21558]:0x3b10f4)
    at mono_interp_exec_method (wasm://wasm/04dd8aba:wasm-function[21548]:0x3a4de7)

Cause: I did not confirm this 100%, but highly suspect the cause to be the fact that EH as emitted by the AOT compiler is translated into WASM's catch_all. catch_all catches all exceptions, even JS ones thrown by Emscripten's exit.

Although, curiously enough, a -c Debug publish, seemingly not using WASM EH, also crashes.

Author:	SingleAccretion
Assignees:	-
Labels:	arch-wasm, area-Codegen-AOT-mono
Milestone:	-

[pavelsavara]

I was able to reproduce, this is jiterp code, assert at

runtime/src/mono/mono/mini/interp/interp.c

Line 2756 in 65b696c

g_assert (obj);

cc @kg

[kg]

I was able to reproduce, this is jiterp code, assert at

runtime/src/mono/mono/mini/interp/interp.c

Line 2756 in 65b696c

g_assert (obj);

cc @kg

That code was added by 3a9085e. It is correct IMO, it just happens to be wrong for this specific platform due to how WASM EH works. So we probably need to handle this scenario (a native exception was thrown but there's no exception object) in a special way.

Though I suppose it is possible this could also occur on say x86-64 if an SEH exception is thrown by a pinvoke and we unwind into the interp without wrapping it in a managed exception first.

[kg]

cc @BrzVlad @vargaz I think the correct fix here would be for the code that traps the exception and sets the 'thrown' flag to notice that a special exception has been caught, and rethrow it instead of trapping it. Does that sound right? I'll need to figure out how we would identify these special exceptions though.

[SingleAccretion]

Note that if you are using WASM EH, then, if you use catch <tag index> instead of catch_all (at LLVM level this means emitting the @wasm.get.exception intrinsic), it won't catch JS exceptions such as the one thrown by exit.

[kg]

Clang is probably already generating catch <tag> for mono_llvm_cpp_catch_exception, right?

void
mono_llvm_cpp_catch_exception (MonoLLVMInvokeCallback cb, gpointer arg, gboolean *out_thrown)
{
	*out_thrown = FALSE;
	try {
		cb (arg);
	} catch (int*) {
		*out_thrown = TRUE;
	}
}

while the jiterpreter uses catch_all, so it probably needs to figure out which tag is used by clang and use the same one somehow...

[kg]

Oh no :(